1. Field of the Invention
The present invention relates to shock absorbers (hydraulic dampers) for the suspension system of a motor vehicle or other mechanical device. In particular, the present invention relates to hydraulic dampers of the single or monotube type.
2. Background Information
The state of the art includes various shock absorbers or hydraulic dampers used mainly for the suspension of a wide variety of motor vehicles. This technology is believed to have significant limitations and shortcomings, including, but not limited to, that the shock absorbers or hydraulic dampers presently in use operate at elevated pressure that causes air to mix with the hydraulic fluid commonly used within these damper devices.
For this and other reasons, a need exists for the present invention. This invention provides a non-pressurized shock absorber that has an extended service life and is easily rebuilt. The non-pressurized shock absorber device of the present invention is believed to fulfill the need and to constitute an improvement over the background technology.
Referring now to FIGS. 1 and 2, known hydraulic dampers of the monotube type are comprised of a tube (body) with a rod guide fixed at one end and a base fixed at the other end of the tube. A piston and rod assembly pass slidingly and sealably through the tube and rod guide, respectively. A floating piston is located slidingly and sealably in the tube between the primary piston and the base. The primary piston divides the tube into two chambers, a rebound chamber to the rod guide side and a compression chamber to the floating piston side. Both chambers are typically filled with hydraulic fluid (oil), which provides lubrication and viscous resistance to linear movement. The primary piston includes valving, which permits fluid to pass through the piston at preset or adjustable flow rates based on the pressure differential between the rebound and compression chambers. The floating piston divides the tube into a third chamber at the base side, which is typically filled with a gas under high pressure. This gas allows for volumetric compensation, as the rod slides in and out of the tube, and provides pressure to force the oil through the primary piston during the compression stroke. A mounting member is secured to the base member, and another mounting member is secured to the exterior end of the rod member. The mounting members fasten the monotube shock absorber device in a operable position on a motor vehicle.
In the arrangement shown in FIGS. 1 and 2, the gas pressure must be sufficient to resist the pressure created in the compression chamber during the compression stroke, or the oil in the rebound chamber will cavitate, which diminishes the damping effect at the start of the rebound stroke. The internal pressure created by the pressurized gas in the third chamber acts on the cross-sectional area of the rod to cause this type of damper to also act as a pneumatic spring, which has a progressive rate as the damper is compressed and the compensation chamber volume is reduced. This spring effect is increased further as the damper's temperature rises. This progressive and temperature dependent spring effect is usually unwanted in a suspension system. Also, as the seal on the floating piston degrades from wear over time, the gas infiltrates into the other chambers, degrading the damping performance of the damper and shortening its useful life.
All United States patents and patent applications, and all other published documents mentioned anywhere in this application are incorporated by reference in their entirety. Some examples of hydraulic damper devices for which patents have been granted include the following.
Willich et al., in U.S. Pat. No. 3,690,425, describe a hydraulically dampened vehicular suspension device that includes a self-contained damper unit which incorporates a shock absorber and which can be easily fitted into a pipe carrying a wheel-axle journal at its lower end. In order to replace the damper unit in the outer pipe, it is only necessary to unscrew a lock nut and uncouple the damping cylinder of the inserted unit from the vehicle chassis. The device may also include a means for cooling the damping cylinder in use.
In U.S. Pat. No. 4,290,511, de Baan et al. disclose a load-carrying, shock absorbing strut comprising an outer tube for carrying a wheel axle journal. Slidably accommodated in the tube is a shock absorber cylinder which is connected with the chassis frame. A downwardly emerging piston rod of the cylinder is fastened to the bottom of the outer tube. Between the shock absorber cylinder and the outer tube there is provided a lubricant annular chamber of constant volume which is closed off above and below by upper and lower guide and sealing rings arranged on the outer tube. A sealing ring is arranged above each guide ring with axially limited play and comprises lubricant-sealing felt rings. To effect good dirt-deflecting action there is present above the upper sealing ring a dirt-deflecting ring which has the dual function of limiting the sealing ring axial play, as well as removing dirt from the shock absorber cylinder.
Gute, in U.S. Pat. No. 4,452,436, describes a single tube vehicle suspension strut with a built-in shock absorber in which the piston rod is formed from tubing that provides a reservoir for shock absorber fluids. The strut further features this type of piston valving with the deflecting spring discs and cooperating metering pin construction, which can readily reduce high pressure build-up and which can be adjusted to provide ride and level control. This unit can be used to provide a leveling feature with the gas spring in the piston tube operatively connected to suitable controls for pressurized gas and exhaust.
In U.S. Pat. No. 4,638,896, Poyser discloses a shock absorber of monotube or twin-tube configuration, where the piston within the shock absorber includes an electromagnetically operable bypass valve, with the electromagnetically operable valve being controlled remotely from the outside of the shock absorber via an electrical connection which extends along the piston rod. In a twin tube configuration according to the present invention, the foot valve assembly also includes an electromagnetically operable bypass valve which is remotely controlled from the outside of the shock absorber via an electrical connection. These electrical connections do not affect the overall design of the shock absorber and can thus be easily included in a vehicle design. Further, these electrical connections can be connected to a microprocessor so that the shock absorber valves are controlled by the microprocessor dependent upon the values of certain parameters, e.g., speed or load, fed to the microprocessor from appropriate sensors.
Jentsch et al., in U.S. Pat. No. 5,570,762, describe a hydraulic damper of the monotube type, in which the floating piston includes a first valve allowing fluid flow from the compression chamber to the compensation chamber when fluid pressure in the compression chamber exceeds that in the compensation chamber by a predetermined amount and a second valve allowing fluid flow from the compensation chamber to the compression chamber when fluid pressure in the compensation chamber exceeds that in the compression chamber by a predetermined amount. The device provides improved high speed damping.
In U.S. Pat. No. 5,678,808, Claude et al. disclose a gas charged monotube strut that carries the accumulator outside the damper's cylinder tube and within the strut mount. A substantially direct flow path is provided between the damper and the accumulator through the damper's piston rod. Air to oil separation is maintained by a gas cup, and a low profile of packaging is provided.
Pees et al., in U.S. Pat. No. 5,706,920, describe a suspension damper of the monotube, gas charged, shock type that includes mating piston and rod guide assemblies and mating piston and gas cup assemblies, where the extension and compression travel of the damper is maximized. The piston includes an annular skirt with a lower rebound cutoff element. The rod guide assembly includes twin, spaced apart, bushing assemblies providing lateral support to the piston rod, a lower annular leg and an upper rebound cutoff element. When the damper is in a fully extended position, the lower annular leg is received within the upper rebound cutoff element, and the upper rebound cutoff element is received within the annular skirt of the piston assembly.
In U.S. Pat. No. 5,984,060 Clark et al. disclose a monotube strut assembly that includes a housing tube with a piston assembly fixed relative to the housing tube by a piston rod. A damper body tube is reciprocally carried in the housing tube and is slidably engaged with the piston assembly. A bearing sleeve is fixed in position within the housing tube, and seals are carried at both first and second ends of the bearing sleeve. A bearing is positioned adjacent each of the first and second ends of the bearing sleeve and the bearings slidably support the damper body tube. A quantity of oil is carried between the damper body tube and the bearing sleeve, providing lubrication between the bearings and the damper body tube.
Johnston et al., in U.S. Pat. No. 6,161,662, describe a monotube suspension damper that including a cylinder tube having a fluid chamber and a gas chamber, and a piston dividing the fluid chamber into a compression chamber and a rebound chamber. Also present is a primary fluid flow path across the piston that includes flow control valves which throttle fluid flow, a secondary fluid flow path across the piston parallel to the primary flow path that includes flow control valves which throttle fluid flow, and a tubular connecting rod on the cylinder tube connected to the piston. A valve spool is supported on the piston for linear translation between closed and open positions blocking and unblocking the secondary flow path. A control rod inside of the connecting rod is disposed between the valve spool and a flexible diaphragm exposed to pneumatic pressure in an expandable load leveling chamber between sprung and unsprung masses of the motor vehicle. As the pneumatic pressure in the expandable chamber varies, the control rod transfers flexure of the diaphragm to the valve spool to close the secondary flow path and increase the stiffness of the suspension damper as pneumatic pressure increases and to open the secondary flow path and decrease the stiffness of the suspension damper as pneumatic pressure decreases.
In U.S. Pat. No. 6,247,563, De Carbon et al. disclose a piston with a valve for a hydraulic damper tube. The piston comprises a piston body having a fluid passage interacting with a floating valve element for controlling in both directions the amount of fluid flowing through the passage. The floating valve element includes a spring washer, the deflection of which in the free state is between approximately 0.1 times and approximately 2 times the thickness of the washer.
Marking, in U.S. Pat. No. 6,311,962, describes a gas spring shock absorber that includes a damping fluid cylinder telescopically housed within a gas cylinder. A shaft connects a sealed, outer end of the gas cylinder with a vented piston movably mounted within damping fluid cylinder. The shaft passes through a sealed inner end of damping fluid cylinder so that a sliding seal located between gas cylinder and damping fluid cylinder creates a sealed variable-volume gas cylinder between the cylinders.
In U.S. Pat. No. 6,318,523, Moradmand et al. disclose a piston valve assembly for regulating the flow of fluid through a monotube fluid vehicle damper. The assembly includes a piston rod and a piston end having opposing first and second surfaces secured to the piston rod by a connector. A first outer annular seat is spaced radially from the piston rod and extends from the first surface. At least one first fluid passageway connects a first opening between the piston rod and the first outer annular seat and the second surface for providing fluid communication there between. A first blow-off valve has a hollow cylindrical portion, with a first flange extending transversely from an end thereof and with the first flange adjacent to the first outer annular seat when the first blow-off valve is in a closed position. The piston rod and connector secure the blow-off valve to the piston end. The first blow-off valve is movable to an open position away from the first surface. A first low speed bypass valve is interposed between the at least one first passageway and the second surface for permitting fluid to exit the at least one first fluid passageway past the first blow-off valve when the first blow-off valve is in the closed position. A first helical spring engages the first blow-off valve for biasing the first blow-off valve to the closed position. The blow-off valve provides increased digressive performance during operation of the damper.
Hofmann et al., in U.S. Pat. No. 6,390,258, describe a guide assembly for a rod of a motor vehicle strut comprising a rod guide, a seal cover, and a retainer. The seal cover engages the rod guide, and defines an area there between. The retainer is engaged with the seal cover. A first O-ring is disposed between the seal cover and the rod guide, and a second O-ring is disposed between the rod guide and the retainer.
Applicant has devised a shock absorber of a monotube type which operates at normal atmospheric pressure. The monotube shock absorber of the present invention provides a variety of advantages over the monotube shock absorbers presently on the market.